Remote sensing pressure control systems are well known in the art for use in water systems such as chilled water, hot water, and process water systems. A conventional remote sensing differential pressure control system, generally designated by the index numeral 10 is depicted in FIG. 1. In control system 10, a pair of chillers 12 and 14 provide chilled water for a recirculating system. On the inlet side of the chillers are two primary pumps 16 and 18, which have a common "return" pipe 20. On the outlet side of the chillers are two secondary pumps 22 and 24, which typically are variable speed pumps driven by a mechanical variable speed devices or electrical variable speed devices. In such a system, a hydraulic bridge 26 is commonly provided to hydraulically decouple the primary pumps 16 and 18 from the secondary pumps 22 and 24.
On the discharge side of secondary pumps 22 and 24 is a common "supply" pipe 28. The supply piping 28 provides fluid to one or more zones, and in FIG. 1 four zones are depicted, having the index numerals 30, 32, 34 and 36. Each zone includes one or more variable volume loads, such as indicated by index numerals 38 and 40, each of these loads including a flow control valve 42 and a cooling coil 44. The variable volume loads for the other zones are indicated by index numerals 60 and 62 (for zone 32), 64 and 66 (for zone 34), and 68 and 70 (for zone 36). Flow control valve 42 can either be a modulating valve or an on/off valve. It will be understood that cooling coil 44 could be replaced by a heating coil in a control system that replaced chillers 12 and 14 with boilers or some other type of water heating source. Water flow direction is generally designated at various locations by arrows associated with the letter "F".
In the situation in which control system 10 is installed in a high-rise building, a differential pressure sensor 46 will typically be installed in the top floor, and its differential pressure lines 45 and 47 are connected on the supply side of control valve 42 and on the return side of cooling coil 44. It will be understood that the physical location of differential pressure sensor 46 can be located elsewhere within zone 30 while maintaining stable system performance, but by locating sensor 46 on the top floor, the lower floors are guaranteed to be provided with at least as much pressure as the top floor.
Differential pressure sensor 46 has an electrical output which is connected to a pump control panel 50 by use of a dedicated electrical cable 48. In order for pump control panel 50 to properly control the speed of variable speed pumps 22 and 24, the output signal provided by differential pressure sensor 46 must be in real time (i.e., virtually continuous, or at least updated twice per second), or pump control panel 50 will not be able to control these variable speed pumps in a stable manner. This aspect of the conventional control system 10 is so important that a typical installation will include a pair of wires between each of the differential pressure sensors 46, as indicated by index numerals 48, 52, 54, and 56.
In a conventional control system 10 which only includes one zone (i.e., there is only one zone of system loads and only one differential pressure sensor 46), there would only be one pair of wires leading from the differential pressure sensor 46 back to pump control panel 50. In this circumstance, pump control panel 50 can directly control the speed of variable speed pumps 22 and 24 from that single electrical signal that represents the differential pressure sensed by differential pressure sensor 46.
In the circumstance where there are multiple zones (as depicted in FIG. 1 ), pump control panel 50 evaluates the zone having the highest hydraulic demand and selects that zone's differential pressure sensor 46 to control the speed of variable speed pumps 22 and 24. This can functionally be implemented using either pneumatic or electronic controls, and in the case of electronic controls it can be implemented using either analog techniques or using digital techniques.
One unfortunate aspect of control system 10 is that in situations where each of the zones 30, 32, 34, and 36 are remotely located from pump control panel 50, the installed cost for wiring the individual differential pressure sensors 46 to pump control panel 50 can be prohibitive. This aspect not only includes the cost of long runs of wiring conduit for each of electrical cables 48, 52, 54 and 56, but also includes circumstances where it would be almost impossible to install such wiring (e.g., in a campus environment, or where the signal must cross a river).
Remote sensing pressure control systems also are well known in the art for use in non-recirculating booster pump water systems, commonly used in municipal and industrial applications such as public water supply systems and sewage systems as well as for other industrial uses. Such conventional systems generally provide more than one pumping station that feeds pressurized water (or other fluid) to a non-recirculating system, in which the key operating parameter is to always maintain a certain minimum pressure at all points in the system's "grid" of users. Such non-recirculating systems generally do not recirculate the water after it has been used or treated, although certain industrial processes may recirculate portions of their fluids after they have been used.
In many cases of non-recirculating systems, the pumping stations are physically many miles apart from one another, and such conventional systems often use hard-wired remote electrical connections (such as dedicated 4-20 mA loops or dedicated telephone lines with pulse-width tone transmitters and receivers) or radio or other electromagnetic radiation-type links to transfer system operating parameters from station to station, as required to operate the system. Many of these communication links are, unfortunately, very expensive to install and/or operate in real time, and the alternative in such convention systems is to have very slow system response. A method of improving system response time that is also cost-effective would be a significant advance in this field of art.